OK-NET Arable Project Challenges of Organic Arable Farming 2nd module: Fertilization strategies to enhance nutrient availability in organic arable crops Module description and objectives Inadequate nutrients supply is often a factor limiting yields in organic farming. In addition to a short introduction of the topic, the course will offer innovative practices and tools allowing for a more efficient use of natural resources and processes in order to improve farm nutrient recycling and to optimize the use of nutrients into the soil. The objective of the module is to present the main problems related to the nutrient management in organic arable farming. Trainees will get information about tools and practices that can help them develop a sound nutrient management plan and enable them to participate in the discussion on this important topic. Some of the tools are site specific and this should be taken into consideration while evaluating them. Module outline 1 - Challenges in nutrient management 2 - Strategies to improve nutrient 2.1 Legumes management 2.2 Cover crops, green manure and intercropping 2.3 Livestock manure 2.4 Compost 2.5 Commercial mineral and organic fertilizers 3 - Calculation tools 3.1 Nutrient budget 3.2 Rotation planning 4 - Future prospects for nutrient sources 5 - Conclusive illustration 1. Challenges in nutrient management The most important bottleneck for plant productivity in organic arable farming is nitrogen. Mixed farms with sufficient livestock can best cope with nitrogen and result in high yields. For stockless farms, mix- and intercropping with legumes is important. Phosphorus deficiencies are a problem of stockless arable crop farms, especially longstanding ones. Worldwide, the commercially available phosphate resources, used to produce phosphorus fertilizer, are decreasing. Improving the bioavailability of poorly soluble mineral sources of P (e.g. rock phosphate) through fermentation or composting with organic materials is becoming subject of research interest. 1. Challenges in nutrient management Organic growing depends first and foremost on the mechanisms in the soils that convert nutrients from non-plant available to plant-available forms in the root zones. Soil fertility → Plant nutrition The second important mechanism is the recycling of organic material and nutrient elements, mostly on-farm, e.g.: • Livestock manure • Green manure • Compost • Field residues Crop rotation covers all aspects above thereby affecting both, soil nutrient availability and plant nutrient uptake. 2. Strategies to improve nutrient management Careful matching of secondary crops with the primary crop and growing conditions (e.g. root systems not competing but supplemental, combinations of nitrogen-fixing with non-fixing crops) is needed, based on plant appearance, timing of growth phases and complementarity of resource and nutrient use. When developing a fertilization plan, several aspects should be taken into account. The example of nitrogen supply for winter oilseed rape shows differences in fertilization strategies depending on the following parameters: - Farm with or without livestock - Previous crop - Timing of fertilizer application Farmers can also create their own trial plots to test different fertilization strategies and to choose the best option for cultivation. 2.1. Legumes Leguminous crops are an important source of nitrogen in organic crop production, in both mixed and stockless farms. On mixed farms, the inclusion of leguminous crops in the rotation serves for: Fixing aerial nitrogen Improving soil fertility and soil structure Delivering feedstuff for ruminants On stockless farms, legumes are mainly important for nitrogen fixation, soil organic matter improvement and soil fertility and are therefore called green manure. 2.1. Legumes Stockless systems commonly use grain legumes as they have a cash value and the usage for feedstuff is economically less important in stockless systems. Realistic N-fixation rates are between 17 and 200 kg N ha-1 year-1 for grain legumes and between 63 and 236 kg N ha-1 year-1 for temperate forage legumes. Grain legumes have considerable higher fixation rates than forage legumes on temporary or permanent grassland but grain legumes consume most N for their own growth. Forage legumes in grassland stands are stimulated by the N consumption of the monocotyledons (grass) and have higher fixation rates than in pure stands. 2.2. Cover crops, green manure and intercropping A wide range of plant species belonging to different botanical families are used as cover crops and green manures. Species should be selected according to farmers’ objectives (e.g. nitrogen fixation, organic matter increase, biofumigation, etc.). Green manures can serve as powerful tool to balance nutrient supply for farms without livestock. This is particularly important when cultivating nutrient demanding plants (e.g. maize). The cultivation of winter field peas and the incorporation in spring as green manure before maize can provide 100 kg of nitrogen to succeeding crops. Green peas are also used for intercropping. Barley as companion crop provides support for peas with significant increase in pea yield. 2.2. Cover crops, green manure and intercropping Tailored use of cover crops as part of rotation can enable farmers to benefit the most of them. When choosing species for cover crops mixture we need to have information about them. Some examples: Lolium perenne is good for building soil structure, to enhance water infiltration and water-holding capacity. Trifolium pretense creates loamy topsoil, adds a moderate amount of N and breaks up heavy soil. Medicago sativa can be good even for arid areas as soil-saving and soil- building species, counting on its ability in N fixation and self-reseeding. Vicia villosa is recognized as an excellent green manure for dry conditions. Based on extensive experiences with cover crops in Denmark, some general conclusions have been drawn for their management in arable rotations. 2.2. Cover crops, green manure and intercropping “Green manuring” involves the soil incorporation of any field or forage crop while being green or soon after flowering, for the purpose of soil improvement. The difference between cover crops and green manures is that cover crop is any crop grown to provide soil cover, regardless of whether it is later incorporated. The practical guide “Sort Out Your Soil”, largely used in the UK, gives a wide overview of green manures with all details about the management and the benefits of their presence in crop rotation. Even though most of organic farmers are familiar with benefits derived from green manure, still in some conditions their incorporation turns out to be a challenge and depends on the cultivation technique of the succeeding crop and the machine used. Here you will find some examples. 2.2. Cover crops, green manure and intercropping Cover crops and green manures can be annual, biennial, or perennial herbaceous plants grown in a pure or mixed stand during all or part of the year. Cover crop management affects the N content of legume cover crops and the contribution of N to the following cash crop. Early establishment of legume cover crops results in greater biomass production and N production. The C:N ratio of grass-legume mixtures is usually intermediate to that of pure stands and this is seen as advantage of mixtures. Beside soil fertility building, cover crops provide ground cover (less erosion), help suppress weeds and reduce insect pests and diseases. Leguminous leys are usually associated with N fixation but when species composition and management are well performed they can deliver additional benefits. 2.3. Livestock manure The prototype of an organic farm is a mixed farm where livestock manure secures the productivity of the arable crops. Nutrients concentration and quality of manure depends on its origin, composition (e.g. with or without straw), period and way of storage, season and moment of application to the soil. An efficient use of nutrient derived from livestock manure requires the knowledge of crop-specific nitrogen demand. Considering nitrogen delivery from livestock manure, the supply varies from season of application and demand, according to the crop. Here, it is important to note that manure application affects actual and succeeding crops. 2.3. Livestock manure At low stocking densities (<< 1 livestock unit per ha) the yield gap is much higher than at high stocking densities (>> 1 livestock unit per ha). The level of yields of organic arable crops receiving livestock manure is often between 80 and 90 percent of conventional crops. As the farms have become more specialized in general, the regional cycles of livestock manure (between livestock and crop producers) are important to be organized. Specialized stockless farms might run into a P deficit and this can threaten yields. Strategies to prevent this include Composts, Regionally available manures, and Commercial fertilizers based on rock phosphate. 2.4. Compost The knowledge on the preparation and application of composts is very heterogeneous among European farmers and generally low. Excellent and easy- to-use information material in national languages is urgently needed. Bio-waste (e.g. food and kitchen waste; waste from food processing plants) accounts for 88 million tons of municipal waste each year in the EU - currently, only 23 % is effectively recycled. Composts play a crucial role in securing the productivity of crops in horticultural and in arable systems of organic farms in that they maintain and enhance the fertility and physical stability of soils. 2.4. Compost Organic waste composts can be returned to soils as fertilizers or soil improvers. Their sustainable use in agriculture reduces the need for mineral-based fertilizers, the production of which has negative environmental impacts and depends on imports of phosphate rock which is a limited resource. Composts from separately collected household bio wastes, when applied in recommended application rates, deliver 5 to 10 kg plant available N per hectare in the first year and 25 to 35 kg in the following ones. In order to compensate for P and K exports from the farm, much lower compost applications are needed.